1. Field of the Invention
This invention relates to a mounting device for centering an angular rotation transducer onto an output shaft of a drive motor.
2. Related Art
Large motors that operate in steel mills, paper mills, rubber mills, or other processing mills require precise speed control to control the rotational speed of the output shaft. Highly accurate transducers are required to provide near instantaneous feedback to the motor controller in order to maintain constant rpm of the output shaft of the motor. Once the precision of the transducer has been established, it is imperative that the center line of the transducer shaft be closely aligned with the center line of the motor shaft. A typical mill motor shaft includes a threaded hole pattern without the benefit of a pilot or counterbore to aid in centering.
Until recently, most feedback transducers were largely foot mounted arrangements, where the transducer shaft had to be aligned to the center line of the motor shaft by adjusting elevation, transverse direction, and runout of the transducer frame in order to achieve proper alignment. A transducer that was not aligned with the motor center line would generate a once-per-revolution error signal in addition to the relative speed feedback signal. The once-per-revolution error signal would then be amplified by a speed loop forward gain and would become the reference for the current loop, resulting in large torque disturbances in the closed loop system.
Shaft-mounted devices, such as that found in U.S. Pat. No. 5,048,384 to Carlen, use set screws at orthogonal axes to each other to center the base of the mandrel shaft that is ultimately connected to a measuring device such as a tachometer. A disadvantage of this type of centering device is that the centering process requires the loosening and tightening of four screws to move the mounting center on an angular trajectory.
What is needed is a system to center a feedback transducer where the center can be moved in a less complicated manner with only two adjustments.